In the assembly of pipelines from individual pipe lengths it is customary to weld the pipe lengths to each other at a butt joint in the field. To hold the abutting pipe sections in position during the welding operation, a plurality of individual clamping devices are clamped in position near one end of one pipe length by a circumferentially extending chain which, when tightened, presses the clamping devices firmly against the pipe. Each clamping device projects beyond the end of the pipe section to which it is clamped and jack screws on the clamping device are adjusted to grip the end of the adjacent pipe length to hold it in aligned abutting relationship with the first pipe length while the joint is welded. Typical examples of clamping devices of this type are shown in U.S. Pat. Nos. 3,593,402; 3,666,159; and 3,704,503.
Most clamping devices of this general type presently in use perform adequately for the formation of joints where the abutting pipe ends lie in general planes perpendicular to the pipe axis, i.e., where the assembled pipe string runs in a straight line. However, problems are encountered by prior art devices in those cases where a mitered joint must be formed, that is, where the two pipe lengths form an angled joint with the axes of two adjacent lengths inclined to one another.
The problem encountered in prior art clamping devices where a mitered joint is to be formed arises due to the fact that most prior art devices rely on the clamping force exerted by the circumferentially extending chain to anchor the device to one of the pipe lengths and rely on the jack screw to anchor the device to the other of the two lengths. Where a mitered or angled joint is to be formed, the axial distance between the points of application of the clamping forces on the respective pipe sections will vary considerably around the circumference of the joint due to the fact that the clamping chain lies in a plane substantially normal to the axis of one of the pipe lengths while the abutting joint lies in a plane which is inclined to the axis of at least one of the two pipe sections. Application of the clamping force as close as possible to the joint is desired, because in many instances the clamping device must not only establish the desired axial relationship between the two pipe sections, but must also be utilized to correct an out-of-round condition of at least one pipe length so as to form an abutting joint around the entire circumference.
The present invention is especially directed to a pipe clamping assembly of the general type discussed above which is useful not only in coaxially aligning abutting pipe lengths, but which is also especially useful in aligning abutting pipe lengths where the abutting joint may lie in a plane inclined to the axis of one or both of the pipe lengths.